Add parent-aware feature guidance

[nikivanstein]

Summary

• extend feature guidance to consider a selected parent's feature vector when computing SHAP contributions and tailor the guidance message
• update mutation prompt construction to request parent-specific guidance without clearing messages when none is available
• add parent-aware feature guidance tests, including extreme feature value scenarios

Testing

• uv run pytest tests/test_feature_guidance.py

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Codex Task

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 26 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
llamea/feature_guidance.py	74.62%	17 Missing ⚠️
llamea/llamea.py	18.18%	9 Missing ⚠️

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